Electrical boxes are used for mounting and connecting a variety of different electrical devices, as well as for connecting wires and cables. The size and shape of the electrical box used are typically determined by the specific application and the location of the installation. Octagonal shaped electrical boxes with four flat sides and four curved sides are commonly used because the four flat sides of the box allow for different orientations. These octagonal shaped electrical boxes are often installed over a vapor barrier membrane, especially for new construction applications. Care must be taken not to damage the integrity of the membrane and, if it is damaged, it must be repaired. This can add to the cost and the time needed to complete a project. FIG. 1 shows a typical roof construction, beginning with a drywall panel that forms the interior ceiling and then successive layers of wood furring, vapor barrier membrane, horizontal trusses, insulation, sloped trusses, plywood roof, roof protective membrane and roof shingles. In energy efficient homes, a vapor barrier membrane (e.g., a polyethylene membrane), is installed between the truss and the wood furring.
There are many ways to install an octagonal electrical box in a ceiling. The most common is to install the box between two wood furring strips and fastened in place with three or four screws. The end-user typically adds a second layer of vapor barrier membrane behind the box to ensure that screws passing through the membrane do not compromise the vapor barrier. The installation becomes more difficult when the structure is formed by pieces of wood that are arranged in a stepped back manner and the octagonal electrical box cannot be easily attached to one of the pieces of wood.
A second method of installing an octagonal box is to install a piece of wood (generally a 2″×4″ piece) between two trusses and securing the octagonal box to it. This piece of wood has to be positioned above the trusses so that the back wall of the box can be affixed to the piece of wood and the front of the box is flush with the finished ceiling. Another way to install an octagonal electrical box is the most time consuming method. The user cuts the membrane and then seals the vapor barrier booth and the membrane with acoustical sealant and tape. After that, the electrician can run the cables to the box and fasten the box on the truss through the vapor barrier booth. If the seal is not perfect, the barrier will not function properly and the installation will become energy inefficient.
Accordingly, there is a need for an electrical box that can be easily mounted to a truss or a support covered by a vapor barrier membrane without puncturing the membrane and compromising the vapor barrier seal.